1) Antibody diversity: Amino acid sequence analysis of anti-galactan myeloma proteins has revealed that these proteins may employ any of the 4 known light chain joining (J) segments. Position 96L which is located in the third complementarity determining region and is coded for by the J gene is apparently not involved in determining antigen binding specificity in this system. In contrast this position may be important in specificity determination for phosphorylcholine binding antibodies. The amino acid found at position 96 in 5/6 of the antigalactan light chains cannot be generated by known nucleic acid sequences and recombination events. A surprisingly large number of amino acid substitutions have been observed in complementarity determining regions of anti-galactan myeloma proteins with only minimal effects on binding affinity and specificity. 2) Analysis of phosphorylcholine binding antibodies has revealed the existence of allelic forms of an entire immunoglobulin variable region. 3) Membrane proteins: Papain fragments of transplantation antigens have been prepared from three herds of inbred pigs and are being chemically and biologically characterized. In addition the I region gene products have been analyzed by two-dimensional gel electrophoresis and preparative isolation attempts are being initiated.